Homo naledi: New human ancestor buried its dead

Maropeng, 10 September 2015 - A new fossil discovery in the Cradle of Humankind, 50 kilometres from Johannesburg, has deepened the mystery around the origins of humankind.
Video: eNCA

An infographic explaining all the features of a newly discovered hominin species Homo naledi. The new species was found in the Rising Star cave in the Cradle of Humankind.
Photo: eNCA

CRADLE OF HUMANKIND – A new fossil discovery in the Cradle of Humankind, 50 kilometres from Johannesburg, has deepened the mystery around the origins of humankind.

The discovery of a new human relative species, Homo naledi, was announced on Thursday by the University of the Witwatersrand, the National Geographic Society and the Department of Science and Technology/National Research Foundation.

The Cradle of Humankind is a Unesco World Heritage Site known for its rich and diverse fossil record.

Parts of 15 individuals of the Homo naledi species were recovered in an area not far from the Sterkfontein Caves, where human ancestors "Mrs Ples" and "Little Foot", were discovered in 1947 and 1994 respectively.

“With almost every bone in the body represented multiple times, Homo naledi is already practically the best-known fossil member of our lineage,” said Lee Berger, research professor in the Evolutionary Studies Institute at the University of the Witwatersrand.

Berger is also a National Geographic Explorer-in-Residence, and led the two expeditions that discovered and recovered the fossils.

PHOTO: Professor Lee Berger inside the expedition operations tent on site near the Rising Star cave system where a new species of hominin, Homo Naledi, was discovered in 2013. Courtesy: University of the Witwatersrand.

A fossil burial ground

The unique factor about this discovery is that the new species appears to have intentionally taken the dangerous journey to bury its dead in the isolated Dinaledi chamber of the remote Rising Star cave.

PHOTO: The entrance to the Rising Star cave system where a new hominin species Homo naledi was discovered in 2013. Courtesy: University of the Witwatersrand.

The fossils, which haven’t been dated yet, lay in a chamber about 90 meters from the cave entrance, accessible only through a narrow opening.

A special team of slender cavers was needed to retrieve them.

The 1,550 fossil elements were discovered in different layers of the ground suggesting to researchers that the species of Homo naledi entered the cave over a long period of time to bury their dead.

Experts say they thought this kind of ritualistic behaviour was limited to modern humans only.

Dr Paul Dirks of James Cook University in Queensland, Australia, says there is evidence that the fossils, which consist of infants, children, adults and elderly individuals, were intentionally placed in an isolated chamber of the cave.

“What’s important for people to understand is that the remains were found practically alone in this remote chamber in the absence of any other major fossil animals,” he said.

Rising Star cave system infographic. Courtesy: University of the Witwatersrand.

As few other animal fossils were found in the same chamber, it’s likely that there were no accidental visitors to this area.

“We explored every alternative scenario, including mass death, an unknown carnivore, water transport from another location, or accidental death in a death trap, among others,” said Berger.

Due to the fact that the fossils were found in isolation, it has also been difficult to determine the actual age of the fossils, because no accompanying plant or animal fossils could be measured for dating.

PHOTO: Professor Peter Schmid inspects one of the first pieces of Homo naledi to be discovered in 2013. Courtesy University of the Witwatersrand.

Homo naledi – neither human nor ape

The new species of human ancestor has also been a surprise for scientists because of its hybrid characteristics.

“Overall, Homo naledi looks like one of the most primitive members of our genus, but it also has some surprisingly human-like features, enough to warrant placing it in the genus Homo,” said John Hawks of the University of Wisconsin-Madison, US, a senior author on the eLife scientific paper describing the new species.

PHOTO: The Crania lateral of the newly discovered hominin species Homo naledi. Courtesy: John Hawks/University of the Witwatersrand.

This human ancestor had a small brain – about the size of an orange. Research shows it was 1.5 metres tall and weighed 45 kilograms.

The teeth and skull are similar to a more recent human ancestor, Homo habilis, but the shoulders are more ape-like.

PHOTO: The hand fossil of the newly discovered hominin species Homo naledi. Courtesy John Hawks/University of the Witwatersrand.

Homo naledi was able to use hand tools and climb trees.

This is evident from the extremely curved fingers, said Dr Tracy Kivell of the University of Kent, UK, who was a member of the team that studied this part of the anatomy.

PHOTO: The foot of the hominin species Homo naledi recently discovered at the Cradle of Humankind. Courtesy: John Hawks/University of the Witwatersrand.

While the hands are human like, the feet are “virtually indistinguishable from those of modern humans,” said Dr William Harcourt-Smith of Lehman College, City University of New York and the American Museum of Natural History, who led the study of the Homo naledi’s feet.

The feet, combined with its long legs, indicate that Homo naledi was able to walk long distances.

“The combination of anatomical features in Homo naledi distinguishes it from any previously known species,” said Berger.

PHOTO: The Rising Star Expedition Camp. Courtesy: John Hawks/University of the Witwatersrand.

Underground astronauts

The fossils were recovered in two expeditions conducted in November 2013 and March 2014, in what was known as the Rising Star Expeditions.

In the first expedition, which took place over 21 days, more than 60 cavers and scientists worked together in what Marina Elliott, one of the excavating scientists, described as “some of the most difficult and dangerous conditions ever encountered in the search for human origins”.

Elliott is one of six women who were selected as “underground astronauts” from a global pool.

Berger issued a call on social media for experienced scientist/cavers who could fit through the 18-centimeter wide cave opening.

PHOTO: The team of cave explorers referred to as underground astronauts. Courtesy: University of the Witwatersrand.

Unsolved mysteries

“This chamber has not given up all of its secrets,” Berger said.

“There are potentially hundreds if not thousands of remains of Homo naledi still down there,” he said.

The age of the fossils will also challenge previously accepted theories about human evolution.

The team of scientists is still working towards measuring an accurate date after three different methods of dating failed.